Poloxamer F127 block copolymers are known compounds and are generally available under the trademark PLURONIC. These block copolymers consist of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO) blocks arranged in A-B-A tri-block structure: PEO-PPO-PEO with end terminal hydroxyl groups. In some instances, unmodified Poloxamer can be used in medical devices such as ophthalmic lenses.
Poloxamers have the following general formula:HO(C2H4O)a(C3H6O)b(C2H4O)aHReverse poloxamers are also known block copolymers and have the following general formula:HO(C3H6O)b(C2H4O)a(C3H6O)bHwherein a and b may be the same or different and are of varying lengths.
Poloxamers and reverse poloxamers have end terminal hydroxyl groups that can be functionalized to be free radical polymerizable ethylenically unsaturated end groups. An example of a free radical polymerizable ethylenically unsaturated end terminal functionalized poloxamer is poloxamer dimethacrylate (e.g., PLURONIC F-127 dimethacrylate) as disclosed in US Patent Publication No. 2003/0044468 to Cellesi et al. U.S. Pat. No. 6,517,933 discloses glycidyl-terminated copolymers of polyethylene glycol and polypropylene glycol. U.S. Pat. No. 8,377,464 discloses polymerizable surfactants and a method of making same.
Poloxamers and reverse poloxamers are surfactants with varying HLB values based upon the varying values of a and b, a representing the number of hydrophilic poly(ethylene oxide) units (PEO) being present in the molecule and b representing the number of hydrophobic poly(propylene oxide) units (PPO) being present in the molecule. While poloxamers and reverse poloxamers are considered to be difunctional molecules (based on the terminal hydroxyl groups) they are also available in a tetrafunctional form known as poloxamines, trade name TETRONIC. For poloxamines, the molecules are tetrafunctional block copolymers terminating in primary hydroxyl groups and linked by a central diamine. Poloxamines have the following general structure:
Reverse poloxamines are also known and have varying HLB values based upon the relative ratios of a to b wherein a and b are as defined above.
Polyethers, such as poloxamers and poloxamines block copolymers, that are present at the surface of substrates have long been known to inhibit bacterial adhesion and to reduce the amount of lipid and protein deposition (non-fouling surface). In the present invention, we provide an improved synthesis of free radical polymerizable ethylenically unsaturated end terminal functionalized poloxamer and/or poloxamine block copolymers (BASF Corp.). The improved synthesis of free radical polymerizable ethylenically unsaturated end terminal functionalized poloxamer and/or poloxamine block copolymers provides improved overall device performance when the block copolymers prepared according to the invention described herein are included in ophthalmic device forming formulations.
It is known the terminal hydroxyl groups of PLURONIC F-127 can be functionalized to provide the desired reactivity/purpose as part of the total monomer mix, before/after polymerization. Most of the materials described in the literature that respond to external stimuli are acrylic group containing molecules. So, for example, acrylated PLURONIC F-127 is of importance in some lens formulation.
Whether to acrylate the terminal hydroxyl groups in poloxamers can be determined by the functional group of the other reactive molecules in the monomer mixture. The acrylation can be achieved by the reaction of (unmodified) poloxamers and poloxamines such as PLURONIC F-127 with methacryloyl chloride or methacryloyl anhydride in the presence of a suitable base. Since PLURONIC F-127 is an EO-PO block copolymer, it is known to be susceptible to possible degradation upon coming into contact with free radicals; thus yielding undesired reaction byproducts such as high molecular weight impurities when produced under commercial manufacturing conditions. In addition, residual reaction solvent(s), inhibitors, inorganic salts and methacrylic acid (MAA) may also remain in the free radical polymerizable ethylenically unsaturated end terminal functionalized poloxamers and reverse poloxamers. An example of a free radical polymerizable ethylenically unsaturated end terminal functionalized poloxamer is poloxamer dimethacrylate (e.g., PLURONIC F-127 dimethacrylate). PLURONIC F-127 DM, (DM meaning dimethacrylate), made by previously known commercial scale synthetic methods resulted in a grade of material which was routinely outside of the manufacturing specifications for use in forming certain medical devices. This is important because these byproducts may be injurious to the desired polymerization of PLURONIC F-127 DM, particularly when they are being used in a monomer mix for contact lens production. Any undesired and/or high molecular weight impurity can greatly interfere with lens processing, as well as properties and/or performance of the commercialized contact lens. Therefore, it is desirable that functionalized block copolymers such as PLURONIC F-127 DM prepared in commercial scale amounts be free of any high molecular weight impurities which are beyond the limits set in the manufacturing specifications.
In the commercial scale synthesis of PLURONIC F-127 DM, 2,6-ditert-butyl-4-methyl phenol (BHT) is added as a free radical inhibitor to minimize the formation of these undesired byproducts. However, this synthesis is still unable to prevent the formation of high molecular weight impurities and inorganic salts. These impurities pose a manufacturing risk during the filtration of a monomer mix for making hydrophilic contact lenses containing same by slowing down the filtering process considerably; and, as a result, premature curing, i.e., polymerization, of the monomer mix commences before the monomer mix is introduced to the mold.
Premature curing (polymerization) of monomer materials is undesirable as it renders the monomer mix unsuitable for preparing the desired final product, e.g. contact lenses, and can cause clogging of machines used to make such products. In particular, when the monomer mix starts to polymerize prematurely it slowly forms a gel, typically from the bottom of the vessel upwards. Some monomer mixtures, however, auto-accelerate and can react quite violently.
Therefore, there is still a need for an improved commercial scale synthetic process for providing a high purity functionalized block copolymers, such as PLURONIC F-127 DM.